Uncontrolled cell proliferation in tumors may result from aberrations in response to or production of peptide growth factors. Secretion of growth factors may produce an autocrine or paracrine loop whereby tumor cells direct their own growth autonomously. The objective of this proposal is to examine the biological function and growth-stimulating activity of two novel peptides (TYR-23-ARG-NH2 and TYR-15-ARG-NH2) which experimental evidence suggests are produced during processing of the Insulin-like growth Factor-I prohormone (IGF-I, Somatomedin C), a growth factor which is produced by many tumor types. The goals of this 3-year proposal are 1) to study and characterize the specific binding of TYR-23-ARG-NH2 to high- affinity receptors in primary normal and malignant human lung cells; 2) to isolate and characterize the receptor for TYR-23-ARG-NH2; 3) to determine if the mitogenic peptide TYR-15-ARG-NH2 acts through its own receptor; 4) to study the production of TYR-23-ARG-NH2 by cells or tissues which produce IGF-I prohormone; and 5) to isolate the gene for the TYR-23-ARG-NH2 receptor if it is a unique protein. Primary normal bronchial epithelial cells and primary lung carcinoma cells derived from solid tumors will be used in colony assays to measure growth stimulation; binding of radiolabeled ligands will be used to detect receptors. The cell line A549- 1, which has been shown to contain high-affinity binding sites for TYR-23- ARG-NH2, will be used in initial purification attempts. Secretion of IGF-I and related peptides will be assayed by radioimmunoassay, receptor binding assay, and Western blot procedures. After purification of receptor for TYR-23-ARG-NH2, oligonucleotide probes will be constructed based on a partial amino acid sequence of the protein and cDNA libraries will be screened to isolate sequences complimentary to the receptor gene. This project will increase existing knowledge of the importance of IGF-I and these 2 novel peptides in lung tumor cell growth and will provide data on the tumor-specificity of autocrine mechanisms. These finding will be useful in the development of therapeutic strategies for treatment of lung cancer.